Magic Stone Gourmet (Maseki Gurume)

Full English name: Magic Stone Gourmet ~I who ate the power of the monsters is the strongest!~Romanji: Maseki gurume ~ mamono no chikara o tabeta ore wa saikyō!~

Description:

In this world, It's only me who can get stronger by eating Magic Stones! At one point, I received an offer to have a smooth life reincarnation from the Goddess-sama... But the skill I got as a prize is Toxins Decomposition EX. Ugh, what a plain skill! It's so pitiful that even my own family makes fun of me... However, one day I realized that because of the effect of this skill, I can eat and gain power from Magic Stones! I've also been notified that I'm the prince from a neighboring country!? What awaits me in the castle are days of experimenting with Magic Stones and training, the perfect environment for me to become the strongest man there is... And to top it off, I received the Magic Stone of Dullahan! The story of a boy on the path to becoming a King while being chased by an assertive fiancee and Female Knights starts here!

Impression
This gives me an impression of being a heartwarming and fuzzy story, more on comedic side of the spectrum.
Protagonist gets reincarnated because the goddess wanted to try her reincarnation skill gacha machine, probably. The protagonist, received a useful skill that allows him to nullify all poison effects, is reborn as the first son of some noble douche-bag with moustache. Eventually a second child is born to a concubine with a holy knight skill. The newly minted little brother quickly becomes douche-bag's new favourite and eventually named heir to the family.
Our protagonist, being a hard core mothercon, is trying his best in both training and studies in order to not make his mother sad. Only to have his efforts gone completely unnoticed and being put even further behind his little brother. When things start to reach the point of no return, protagonists mother decides "fuck it, lets go home".
She revealed her true identity, being the second princess of one of the biggest and most technologically advanced kingdom.
Oh and there is the fact that protagonist can absorb stats and skills from magic stones collected from monsters. But 4 manga chapters inn and he has yet to figure out the extend of his ability. I wonder how the protagonist is going to abuse his absorption ability to break the common sense?

Welp, turns out the royal family is a mix blood. With first princes being born a cat sith and protagonist mother being born a dryad. The same went for protagonist so he inherited the dryad skill of absorbing magic from magic stones, or something.